The present invention relates to counterbalances devices used with articulated doors. More specifically, the present invention relates to a counter-balance for use in an articulated door wherein the counter-balance has a strap that rolls up upon itself as the door is opened.
Beverage trailers and trucks having beverage bodies have long been used to deliver beverages to various sorts of retailers. Articulated doors are typically used on both sides of a beverage body to permit access to individual storage bays where the beverages are stored. Under normal use, these doors are opened many times during the day as the driver delivers beverages to retailers along his route. While a general purpose delivery truck may use one roll-up door at the rear of the truck, a typical beverage body may use ten or more doors. Therefore, any disadvantage associated with a particular door design is multiplied many times when that design is employed in a beverage body.
Beverage bodies have typically employed articulated doors that are formed from a sequence of solid aluminum panel sections. These panel sections are formed with interlockable edges. Usually an aluminum panel section will have a first interlockable edge with an attached cylindrical structure and a second interlockable edge opposite the first edge with an attached cylindrical structure having a radius larger than the radius of the cylindrical structure attached to the first edge. The smaller cylindrical structure of a panel section is placed within the larger cylindrical structure of an adjacent panel section thereby forming a joint that allows the two adjacent panel sections to be positioned at varying angles with respect to each other. The smaller cylindrical structure also includes a hollow center in which rollers are inserted. Therefore, every joint typically has a corresponding pair of rollers.
To guide an articulated aluminum door between an open position and a closed position, a door guiding track is required. A typical door guiding track is comprised of a pair of channels, with each channel having a pair of channel members facing each other across a gap in which the rollers are inserted. These channel members also may include track liners, often formed of stainless steel, to absorb vibrational energy and to reduce friction between the rollers and the channel members.
There are several problems that arise from using this type of articulated aluminum door in a beverage body. When doors of this type are new they typically work fine. However, as the beverage body is used, the door frame can be deformed by backing into loading docks and driving over rough roads and curbs. When the door frame is deformed, the door guiding track becomes out of square and the door will either jam or become very difficult to raise and lower.
As the beverage body is transported over roads with the articulated doors closed, the doors vibrate in their tracks. This vibrational energy is absorbed by the rollers and channel members as they vibrate against each other. This forms flat spots on the rollers and indentations in the channel members at the points where the rollers contact the channel members. As these indentations grow in size, the space surrounding the rollers increases, allowing the vibrations to increase in intensity and thereby increasing the rate at which the rollers and channel members deteriorate. These indentations also contribute to the door becoming more difficult to raise and lower.
As a door becomes more difficult to raise and lower, the rollers and channel members are lubricated. The lubrication eventually picks up dust and dirt which further accelerates the deterioration of the rollers and door guiding track. A delivery person will progressively exert more force to open and close the door as this deterioration cycle continues. Eventually a point will be reached when the delivery person will no longer be able to move the door. At this point the beverage body is brought back to the warehouse where typically a forklift is used to unjam the door, which usually destroys the door.
Because aluminum is not a resilient material, collisions with an articulated aluminum door usually result in a partial or complete destruction of the door. This can happen in a warehouse, where forklifts maneuver around and load beverage bodies, in an on-street accident, or from within the beverage body itself if the beverages contained therein should tip over. While the door can sometimes be repaired by replacing the impacted panel section, often adjacent panels will be deformed from the force transmitted through the interlocking edges.
When using beverage bodies in cold climates, the storage bays must be heated to prevent the beverages from freezing. Typically this is accomplished by circulating heated engine coolant from the tractor through the floor of the beverage body. Because aluminum is a highly thermo-conductive material, a layer of insulation must be added to the inner surface of an articulated aluminum door to retain the heat in the beverage body. This adds significant expense, complexity, and weight to articulated aluminum doors used in beverage bodies.
Another problem associated with the use of beverage bodies in cold climates results from the salt and sand that is applied to road surfaces to melt ice and improve traction. The salt and sand work their way into the joints that connect adjacent panel sections, where they corrode and wear down the aluminum surfaces that form the joint. While the door can be steam cleaned, the joint has usually been damaged by the time this is done. Eventually the joint will lock up and the affected panel sections must be replaced.
Because of the weight of an articulated aluminum door, a counter-balance device is typically used to assist the delivery person in opening and closing the door. This device is usually located above the storage bay and is generally comprised of a spring loaded drum that spans the width of the door opening. A cable has one end attached to the center of the drum and another end attached to the bottom of the door. As the door is moved from the closed position to the open position, the cable wraps around the drum in a single layer.
As the door is initially lifted from the closed position, the counter-balance pulls the door straight up. However, as the door continues to move toward the open position, the cable tends to move toward one side of the door opening as it wraps around the drum, thereby applying an asymmetric force to the door. This asymmetric force causes the door to wear excessively in two locations, the top corner of the door adjacent the side toward which the cable is moving and the bottom corner of the door adjacent the side opposite the side toward which the cable is moving.